Reclosable Microwave-Suitable Packaging

ABSTRACT

The invention relates to a packaging suited for heating in microwave ovens, ovens or double boilers, which is comprised of a multilayer film material having at least one area that is rendered permeable when an internal pressure generated by the microwave heating is exceeded. The invention is characterized in that this area is formed by a microperforation that is covered by a label or by a hot stamping film or by a varnish coating.

The inventions relates to a packaging for foodstuffs, ready-to-serve meals, animal feed, non-food products like cold-hot packs, packaged refreshing towels, detergents, cleaning agents, and the like which is suitable to be used in a microwave, oven, or in a water bath.

Foodstuffs or ready-to-serve meals are known which are heated in their packaging, in particular in a microwave, or an oven, or a water bath.

Packagings are understood to mean rigid, semi-rigid, or flexible packagings.

On account of the expansion of the contents and of air and gases associated with the heating up, such packagings tend to rupture or burst.

To a limited degree, this danger can be reduced by using packagings which definitely have larger dimensions than the volume of the contents.

Furthermore, the water contained in the contents is converted to steam during heating. This steam cannot escape from the usual sealed packagings, or only with difficulty; therefore, ready-to-serve meals cannot be heated in such a way that they are crispy.

From EP 661 219 B1 a packaging is known which has a multi-layer structure. In this structure, the exterior layer and the interior layer can be non-heat fused together with one another. Moreover, a connecting part is provided through which the exterior layer is connected to an interior layer by a connecting part and an area in which the exterior layer is not connected to the interior layer so that a communicating passage is formed which has an outlet opening to the exterior space.

The interior side is designed with aids which connect the interior space with the communicating passage. The outlet opening has an adhesive layer which opens when a specific pressure in the interior space of the packaging is exceeded.

As a result, a specific excess pressure is guaranteed in the packaging when it is heated in the microwave. In addition, a controlled escape of the excess pressure is guaranteed from a specific value on.

From WO 03/051745 a packaging of an unopened heatable material, in particular heatable in a microwave, is known which has at least one sealing area which becomes permeable locally when a specific internal pressure is exceeded, this sealing area having at least one passage section which forms a control valve for the packaging contents, and which is designed as a channel-like passage, and which includes a point facing the interior of the packaging, this point preferably being sealed.

A disadvantage of this valve design is that the valve is not only opened from the interior by excess pressure induced during heating but is also easily opened as a result of mechanical pressure. Furthermore, the dimensions of the passage channel cannot be designed precisely. Moreover, the possibility exists that during manufacture, autoclaving, sterilization, storage, or heating, contents migrate from the packaging into the valve pushing open the valve prematurely and exiting into the surrounding space of the microwave oven. However, it is also possible that the valve become clogged with the infiltrating contents and the steam cannot escape to the required degree. In addition, the valve must be located in the area of a sealing seam and cannot be placed freely in another area of the film.

From WO 04/13015 A a packaging is known which has an absorber to absorb the moisture escaping during heating, which allows for the preparation of crispy food. Without a valve through which the excess steam can escape, however, the absorber is used up too quickly.

None of these packagings can be resealed once they are opened and, therefore, cannot be stored, for example in the refrigerator, after having been opened and part of the contents removed.

The purpose of the invention was to make available a packaging suitable for heating in the microwave, oven, or water bath in which, on the one hand, it is possible to develop a specific excess pressure and to allow the steam to escape in a controlled manner and it is possible to cook the food with steam.

Therefore, the object of the invention is a packaging suitable for heating in the microwave, oven, or water bath consisting of a multi-layer film material having at least one area which becomes permeable when an internal pressure produced by the heating is exceeded characterized by this area being formed by a microperforation which is covered by a hot stamping film or a varnish coating.

The microperforation can be produced in the film material by means of needles or a laser beam.

The shape of the microperforated area can vary and, for example, be a circle, rectangle, square, trapezoid, triangle, an ellipsis or semi-ellipsis but also be shaped like specific marks, symbols, lines, letters, text, and the like.

The shape of the microperforation can be a circle, slit, rectangle, square, and the like.

The arrangement of the circles, slits, rectangles, or squares and the like of the microperforation can, if appropriate, form a logo and the like.

In this regard the dimensions of the microperforation can be 10 μm to 1.5 mm in length and/or width, preferably 50 μm to 1 mm. If necessary, a further film can be laminated—at least in the microperforated area—over a varnish or adhesive varnish which softens when exposed to heat, this further film having mircroperforations offset to the first microperforations.

This results in a temporally and locally offset opening of the microperforated valve.

The microperforated valve can be placed at any spot on the packaging.

The microperforated area is covered with an adhesive label, a hot stamping film and/or a varnish coating.

The varnish coating can be a watery as well as solid varnish systems, in particular also a varnish system based on polyester acrylate or epoxyacrylate colophonium, acrylate, alkyde, melamine, PVA, PVC, isocynate, urethane systems, butadiene, a styrene system, or their copolymers, which can be hardened conventionally or reactively (by chemical or radiation hardening).

If necessary, the varnish or the label covering the microperforation, the hot stamping film or varnish coating also contains energy-absorbing additives, like metallic additives, graphite, energy-absorbing pigments or particles and the like. In particular, particles and pigments are considered whose molecular components resonate and are set into thermal vibration as a result of the incident microwave radiation or with which currents are induced by the incident microwave radiation.

These include especially pigments or particles which contain molecular water, like water glass or zeolites. Furthermore, known conductive polymers can also be used.

The varnish coating can be applied to the microperforated area by known coating or printing processes, by gravure printing, flexographic printing, screen printing, offset printing, digital printing, smooth rolling, half-tone or line screen processes—in each case running in the same direction or in the opposite direction—curtain coating and the like.

When heated in the microwave, the varnish layer, the adhesive layer of the label, or the hot stamping film over the microperforated area becomes brittle and, therefore, permeable; the steam produced can escape.

Cooling of the packaging results in the microperforation being resealed by the cooling varnish.

In addition, the microperforation can be resealed by mechanical pressure, for example by pressing the adhesive label on the microperforation again. In this regard the label can be equipped with an adhesive coating which adheres firmly in a specific area outside of the microperforation during heating but loosens in the area of the microperforation during heating. When cooled, this adhesive coating becomes capable of adhering again, and the label can be reconnected to the film by means of mechanical pressure.

Consequently, the packaging can be resealed and, for example, stored until it is used again, if necessary under refrigeration.

The film material of the packaging consists of two or more layers.

The external layer preferably consists of a film made of plastic, for example polyester, like oriented PET, amorphous PET, polyolefines, like polypropylene, cast PP, blown, stretched, biaxially stretched PP films, or polyethylene, polystyrene, polycarbonate, cellophane, polyamide, polyvinylchloride, or their copolymers. However, co-extruded or laminated plastic composite films or composites with paper can be used. Moreover, it is possible to use coated films, biologically degradable films, aluminium foils, and the like. The thickness of the external layer is preferably 8-200 μm.

The inner layer preferably consists of a sealable medium, for example of plastic films made from polyolefines, like polyethylene, polypropylene, from EVOH, EVA, and/or their copolymers or terpolymers, polystyrene, polycarbonate, cellophane, polyamide, polyvinylchloride. However, the inner layer can also be produced by an extrusion coating or varnishing the external film with one of the plastics named.

The thickness of the inner layer is preferably 0.5-100 μm.

If necessary, intermediate layers can be situated between the external and internal layers. Such intermediate layers can be, for example, barrier layers, like aluminium oxide layers or silicone oxide layers, organic barrier layers, like polyamide layers, absorber layers, for example gas absorber layers, like O², CO² absorber layers, water-vapour-absorber layers, ethylene absorber layers, imprinted layers, layers which provide increased flexibility, or strength, or stiffness, and the like.

The entire laminar composite of the inventive packaging can, if necessary, comprise several intermediate layers and combinations of these intermediate layers, in which case the layers either adhere well to each other or can be connected to one another by adhesive aids, like adhesive agents.

In order to identify the opening of the microperforated valve, a marking can be applied around this area on the film material and covering material which clearly changes its appearance upon the area becoming permeable.

For example, two differently coloured markings can be applied which produce a mixed colour in the covered state. After the valve is opened, the two layers separate and the pure colours appear.

Furthermore, in order to identify the opening of the valve, partial information can be applied to the separating layers which then becomes comprehensible information after the valve is opened, for example text, e.g. “open” and the like. This can be done using auxiliary layers with different adhesive strengths.

In addition, one or more absorber layers for the water vapour resulting during heating can be provided on the side of the interior layer facing the interior of the packaging. For example, hydrophilic polymers, like EVA, polymers with high zeolite loadings, silica gel, fleece or fabrics which have embedded hydrophilic polymers, fleece or fabrics coated with zeolite are considered as such absorber layers.

In one embodiment the absorber layer can be applied on the interior layer using pressure processes.

However, the absorber layer can also be fixed to the interior layer with a thin sealing layer or membrane. The fixing layer or the membrane can have a rupture point. When a specific pressure is exceeded in the packaging, the membrane expands and tears open at the rupture site, as a result of which the absorber layer is exposed and the resulting water vapour can be absorbed.

Under such a membrane, perhaps additional membranes, aromatic materials, for example smoked materials or the like, can be present in place of the absorber layer which are then released by the opening of the membrane when a specific pressure is exceeded.

In order to produce a characteristic aroma, aromatic materials in capsules can also be placed in the valve area and released when the valve opens.

Moreover, the packaging can have an opening aid, preferably resealable, for example a laser perforation, a tear string, in which case this opening can then be reclosed by applying a label.

When applying a laser perforation, both the microperforation of the valve as well as the opening aid can be applied by modulating the laser energy in an operational cycle.

However, zipper-like or sliding-closure-like devices, which are resealable, are also opening options.

The packaging can be designed in the shape of a bag, a purse, a stand-up bag, a tray, a sachet, a pouch, or of a sealing film for containers. 

1) Packaging suitable for heating in the microwave, oven, or water bath consisting of a multi-layered film material having at least one area which becomes permeable when the internal pressure produced by the microwave heating is exceeded characterized by this area being produced by a microperforation covered by a label, hot stamping film, or a varnish coating. 2) Packaging in accordance with claim 1 characterized by the microperforated area having, for example, the shape of a circle, rectangle, square, trapezoid, triangle, an ellipsis or semi-ellipsis, but also the shape of specific marks, symbols, letters, text, and the like. 3) Packaging in accordance with one of claims 1 or 2 characterized by the microperforation being shaped like a circle, a slit, a rectangle, a square, and the like. 4) Packaging in accordance with one of claims 1 to 2 characterized by the microperforation being shaped like a logo. 5) Packaging in accordance with one of claims 1 or 2 characterized by the microperforated area having a varnish coating based on a mixture or a polyester acrylate, or epoxyacrylate colophonium, acrylate, alkyde, melamine, PVA, PVC, isocynate, urethane systems, butadiene, a styrene system, or their copolymers. 6) Packaging in accordance with claim 3 characterized by the varnish coating, the label, or the hot stamping film containing an energy-absorbing additive. 7) Packaging in accordance with one of claims 1 to 4 characterized by intermediate layers being provided between the external and internal layers. 8) Packaging in accordance with claim 5 characterized by the intermediate layers being barrier layers, absorber layers, browning layers, [layers which provide] flexibility, or strength, or rigidity, and/or printed layers. 9) Packaging in accordance with one of claims 1 to 6 characterized by the side of the interior layer facing the interior space of the packaging having an absorber layer which is fixed in place by a membrane with a rupture site. 10) Packaging in accordance with one of claims 1 to 7 characterized by different markings being applied to the area of the microperforation which show a definite change in the optical image after the valve is opened. 11) Film material for the manufacture of packagings in accordance with one of claims 1 to
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